5 For there is one God, and there is one mediator between God and men, the man Christ Jesus, 6 who gave himself as a ransom for all, which is the testimony given at the proper time. 7 For this I was appointed a preacher and an apostle (I am telling the truth, I am not lying), a teacher of the Gentiles in faith and truth.
Jesus is our Mediator. This is connected to Him being The Man. A mediator is "One that mediates between parties at variance to reconcile differences."* In order to be the perfect Mediator, He needed to be both God and Man. He had to be the sacrifice and the One making the sacrifice. He had to be of enough value and influence with God to be the One God would accept and deal with. He had to be One God could trust to make and agreement just for both sides of the table. The writer of Hebrews spells this out in explaining what a superior High Priest Jesus was to any other priest ever. In the Old Testament all of the great men who God used to Mediate between God and man: Moses, the Prophets and the priesthood all fell short of being the Perfect Mediator that Christ and Christ alone is. Returning to the context of Paul's challenge here: since we have the Perfect Mediator, let us go to God through Him in prayer.
*(Diann Cotton: 100 Days with Jesus)